U.S. Pat. No. 4,728,981 issued Mar. 1, 1988 to K. C. Koek et al shows an LED printhead assembly. The assembly includes a linear lens array and a printhead. The printhead includes a conventional linear array of LED's on a suitable support (generally with a transparent faceplate and a cooling means). The patent discloses a mechanism for mounting the LED printhead and the lens structure with respect to each other and also with respect to a web-type electrophotographic apparatus. That particular mounting structure is used commercially on high-speed, high-volume, non-impact printers. In this prior assembly the lens structure is mounted on a pair of stiffeners which are then attached directly to the printhead. Thus, the lens array is supported by the printhead.
Our co-pending application Ser. No. 273.770 entitled ASSEMBLY CONTAINING A LINEAR FOCUSING MEANS AND METHODS OF MAKING SAME, filed on Nov. 21, 1988 shows an improvement in the mounting structure over the Koek et al device in which the linear printhead and the focusing means are fixed with respect to each other by fixing a lens stiffener holding the focusing means to a flange connected to the printhead. The focusing means and printhead flange are connected by special screw and washer fasteners that allow adjustment of their relative positions prior to adhesively affixing the washers to the flange. With this arrangement precise optical location of the printhead and focusing means can be obtained very inexpensively. A gap between the heads of the screws and the washers provide thermal compensation for the greater heating up of the printhead compared to the focusing means during operation.
In each of these structures the printhead and the focusing means are optically fixed with respect to each other by precisely connecting them together and the resulting assembly is mounted in the apparatus by connecting one or the other of the previously mentioned components directly to a printer frame at a position known to be correct for proper focusing of the LED's onto the appropriate surface. Because these structures are designed to rigidly fit in the frame of the printer they are reasonably resistant to displacement because of gravity or other forces associated with the mechanism.